12/6 The Rolling Stones released their "Beggars Banquet" album this day in 1968 and one year later on 12/6/69 The Hell's Angels rioted at a show in Altamont, California. Here is the story from Wikipedia:
The event is best known for considerable violence, including the stabbing death of Meredith Hunter and three accidental deaths: two caused by a hit-and-run car accident, and one by LSD-induced drowning in an irrigation canal. Scores were injured, numerous cars were stolen and then abandoned, and there was extensive property damage.
The concert featured (in order of appearance): Santana, The Jefferson Airplane, The Flying Burrito Brothers and Crosby, Stills, Nash & Young, with the Rolling Stones taking the stage as the final act. The Grateful Dead were also scheduled to perform following CSNY, but declined to play shortly before their scheduled appearance due to the increasing violence at the venue. "That's the way things went at Altamont—so badly that the Grateful Dead, prime organizers and movers of the festival, didn't even get to play," staff at Rolling Stone magazine wrote in a detailed narrative on the event, terming it in an additional follow-up piece "rock and roll's all-time worst day, December 6th, a day when everything went perfectly wrong."